1. Field of the Invention
The present invention relates to an image forming apparatus for forming characters or a graphic image on a record medium, and more particularly to an image forming apparatus for forming the image by a light.
2. Description of the Prior Art
In a prior art image forming apparatus such as a conventional copying machine, an original sheet mounted on an original sheet table made of a transparent material is illuminated from the bottom of the original sheet table and a reflected light representing densities of the original sheet is condensed by an optical system including a lens to focus an image of the original sheet on a photosensitive drum.
On the other hand, a liquid crystal display device is used as an image output device for a computer. By mounting the liquid crystal display device on the original sheet table with the display screen of the display device being faced to the plane of the original sheet table, generating the image on the display screen and effecting the copy operation of the copying machine, a hard copy of the display image of the liquid crystal display is formed.
FIG. 1 shows a copying machine capable of forming such a hard copy. It shows a perspective view of an image processing apparatus comprising a combination of a liquid crystal display device and a copying machine with a liquid crystal display screen being attached to a cover of the copying machine.
Numeral 1 denotes an electrostatic photographic plain paper copying machine, and numeral 2 denotes a cover-shaped display device with a display screen 3 being constructed to cover an original sheet table 4. The display device 2 is connected to a personal computer 5 with a keyboard through a cable 6.
Thus, the display screen is used for a console output of the computer 5, processed information is displayed on the display screen 3 and the cover-shaped display device 2 is folded down after the display content has been checked by an operator, and a copy operation is started so that a hard copy of the display content is readily formed. When the computer 5 is used as a word processor, a text displayed on the display screen 3 is corrected and checked and then a hard copy can be formed. Accordingly, operability and copy efficiency are improved. In a system which uses a local area network (LAN) to connect a plurality of computers to transfer information, image information can be transferred between offices, the image information is displayed on the display screen 3, the display content is checked and only the necessary information may be recorded as a hard copy. When the display screen 3 is kept wholly blank, the copying machine 1 can be used to copy a conventional document. Accordingly, it serves as multi-purpose office equipment.
The liquid crystal display device used as the display screen includes two types, a reflection type and a transmission type. The reflection type has a reflection plate arranged on a back side of the liquid crystal display device and the transmission type has a light source arranged on the back side. Neither type provides high contrast images.
Even if the displayed image has a high contrast when it is visually observed, the contrast is insufficient to make a copy of the image on the liquid crystal display and the image of the copy is very hard to distinguish. This is caused by a low sensitivity of the photoconductor.
When the image is displayed with an optimum intensity to the copy operation (which is fairly higher than the optimum intensity for the normal display), it is too glaring for a human eye because the background is too bright, and outlines of characters or images are not sharp because light diffracts into edges of the characters or images.